The present invention relates to printing systems. More specifically, the present invention relates to inkjet printing systems and other printing systems that deposit dots of ink on printing media.
Inkjet printing technology is used in a wide variety of products. Commercial products include printers, graphics plotters, copiers, facsimile machines, and all-in-one machines.
A typical color inkjet product prints with four basic colors: cyan (C), magenta (M), yellow (Y), and black (K). Low end printers, for example, usually include four pens, one for each color (a typical pen, also referred to as a printhead, includes one or two columns of vertically-oriented nozzles, and each nozzle ejects a color ink dot when thermally actuated).
High end printers, in contrast, usually include more than one pen for cyan and magenta. For example, a six-pen printer might have a dark cyan pen, a light cyan pen, a dark magenta pen, a light magenta pen, a yellow pen, and a black pen. Thus this six pen printer uses different shades of cyan and magenta. Higher quality pictures can be produced by using inks having different colorant loads for cyan and magenta.
The different shades can be achieved by using inks having different colorant loads. For instance, different shades can be achieved by using inks having different dye loads or pigment loads. Dark cyan has a higher colorant load than light cyan, and dark magenta has a higher colorant load than light magenta.
During a printing operation, a sheet is moved along a paper flow axis. Each pen may be scanned across the sheet in a scan direction. As each pen is scanned across the sheet, it lays down a swath of ink dots.
If dots are misplaced, they tend to clump together. The clumping can cause edges of the swaths to become visible and horizontal streaks to appear. These visible artifacts are commonly referred to as xe2x80x9cbanding.xe2x80x9d The banding tends to degrade image quality.
As nozzles are fired repeatedly, they become hotter and hotter. As the temperature rises, drop volume variation increases and color shifts result. The color shifts also tend to degrade image quality.
It would be desirable to reduce the banding and the color shifts.
One aspect of the present invention is a method of printing with first and second inks of the same color but different colorant loads. The method includes using a higher ink drop weight for the lower colorant load ink and a lower ink drop weight for the higher colorant load ink.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the present invention.